U.S. patent number 10,437,008 [Application Number 15/663,099] was granted by the patent office on 2019-10-08 for prism unit.
This patent grant is currently assigned to FUJIFILM Corporation. The grantee listed for this patent is FUJIFILM Corporation. Invention is credited to Kazumi Koike, Arihiro Saita.
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United States Patent |
10,437,008 |
Saita , et al. |
October 8, 2019 |
Prism unit
Abstract
In a color separation prism that includes a first and second
prism blocks bonded to each other, the first and second prism
blocks are bonded to the first and second adhesive portions of the
first and second base plates, respectively. The first and second
base plates are fixed to the first and second base plate-fixing
portions of a base with the first and second base-fixing portion
interposed therebetween, respectively. The second adhesive portion
is disposed between the first and second base plate-fixing portions
so that a direction in which the second base plate-fixing portion
is displaced from the first base plate-fixing portion and a
direction in which the second adhesive portion is displaced from
the second base-fixing portion are opposite to each other in a case
in which the base and the second base plate expand or contract due
to a change in temperature.
Inventors: |
Saita; Arihiro (Saitama,
JP), Koike; Kazumi (Saitama, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
N/A |
JP |
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Assignee: |
FUJIFILM Corporation (Tokyo,
JP)
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Family
ID: |
56543033 |
Appl.
No.: |
15/663,099 |
Filed: |
July 28, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170329100 A1 |
Nov 16, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2016/050077 |
Jan 5, 2016 |
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Foreign Application Priority Data
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Jan 30, 2015 [JP] |
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2015-016667 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
5/04 (20130101); H04N 9/097 (20130101); G03B
21/14 (20130101); G03B 17/17 (20130101); G02B
7/1805 (20130101); G03B 33/04 (20130101); G02B
27/1013 (20130101); G02B 27/126 (20130101) |
Current International
Class: |
G02B
7/18 (20060101); G03B 17/17 (20060101); G02B
27/10 (20060101); H04N 9/097 (20060101); G03B
21/14 (20060101); G02B 5/04 (20060101); G03B
33/04 (20060101); G02B 27/12 (20060101) |
Field of
Search: |
;359/831
;348/337,338 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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61-153124 |
|
Sep 1986 |
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JP |
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7-084175 |
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Dec 1988 |
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JP |
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63-298202 |
|
Dec 1988 |
|
JP |
|
1-081613 |
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May 1989 |
|
JP |
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9-000310 |
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May 1997 |
|
JP |
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2001-042204 |
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Feb 2001 |
|
JP |
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2007-292924 |
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Feb 2001 |
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JP |
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2008-298960 |
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Dec 2008 |
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JP |
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2009-271222 |
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Nov 2009 |
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JP |
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2014-217033 |
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Nov 2014 |
|
JP |
|
Other References
International Preliminary Report on Patentability (PCT/IPEA/409)
issued in PCT/JP2016/050077, completed on Oct. 17, 2016. cited by
applicant .
International Search Report (PCT/ISA/210) issued in
PCT/JP2016/050077, dated Apr. 5, 2016 cited by applicant .
Written Opinion (PCT/ISA/237) issued in PCT/JP2016/050077, dated
Apr. 5, 2016. cited by applicant.
|
Primary Examiner: Shafer; Ricky D
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a Continuation of PCT International
Application No. PCT/JP2016/050077 filed on Jan. 5, 2016 claiming
priority under 35 U.S.C .sctn. 119(a) to Japanese Patent
Application No. 2015-016667 filed on Jan. 30, 2015. Each of the
above applications is hereby expressly incorporated by reference,
in their entirety, into the present application.
Claims
What is claimed is:
1. A prism unit comprising: a composite prism that includes a first
prism block and a second prism block bonded to each other, the
first prism block including at least one prism and the second prism
block including at least one prism; a first base plate that
comprises a first adhesive portion and a first base-fixing portion,
the first prism block being bonded to the first adhesive portion; a
second base plate that comprises a second adhesive portion and a
second base-fixing portion, the second prism block being bonded to
the second adhesive portion; and a base that comprises a first base
plate-fixing portion and a second base plate-fixing portion, the
first base-fixing portion of the first base plate being fixed to
the first base plate-fixing portion and the second base-fixing
portion of the second base plate being fixed to the second base
plate-fixing portion, wherein the second adhesive portion is
disposed between the first base plate-fixing portion and the second
base plate-fixing portion, and a direction in which the second base
plate-fixing portion is displaced from the first base plate-fixing
portion and a direction in which the second adhesive portion is
displaced from the second base-fixing portion are opposite to each
other in a case in which the base and the second base plate expand
or contract due to a change in temperature, in a case in which a
line passing through a center of a panel surface of an image
forming panel adjacent to the composite prism and perpendicular to
the panel surface is set as an optical axis, the first and second
prism blocks of the composite prism are bonded to each other so as
to form an air layer in a region including the optical axis, and
the first and second prism blocks of the composite prism are bonded
to each other with a spacer interposed therebetween in a region
other than the region including the optical axis.
2. The prism unit according to claim 1, wherein in a case in which
a linear expansion coefficient of the base is denoted by .alpha.,
an equivalent linear expansion coefficient of the second base plate
is denoted by .beta., an equivalent linear expansion coefficient of
the composite prism is denoted by .gamma., a distance between the
first and second base plate-fixing portions is denoted by L mm, a
distance between the second base-fixing portion and the second
adhesive portion is denoted by M mm, and a change in the
temperature of the prism unit up to 70.degree. C. from 25.degree.
C. is denoted by .DELTA.T.degree. C., a relationship of
".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4" is satisfied.
3. The prism unit according to claim 2, wherein the first base
plate has a linear expansion coefficient equal to the linear
expansion coefficient of the first prism block.
4. The prism unit according to claim 3, wherein the second base
plate includes a first component and a second component bonded to
each other, the first component comprises the second adhesive
portion and has a linear expansion coefficient equal to a linear
expansion coefficient of the first base plate, and the second
component comprises the second base-fixing portion and has a linear
expansion coefficient higher than the linear expansion coefficient
of the base.
5. The prism unit according to claim 4, wherein a difference
between a position of the center of the first adhesive portion and
a position of the center of the first base-fixing portion is within
.+-.5 mm.
6. The prism unit according to claim 3, wherein a difference
between a position of the center of the first adhesive portion and
a position of the center of the first base-fixing portion is within
.+-.5 mm.
7. The prism unit according to claim 3, wherein the first
base-fixing portion is formed of a bolt hole and the first base
plate is fixed to the first base plate-fixing portion of the base
by a first bolt, and the second base-fixing portion is formed of a
bolt hole and the second base plate is fixed to the second base
plate-fixing portion of the base by a second bolt.
8. The prism unit according to claim 2, wherein the second base
plate includes a first component and a second component bonded to
each other, the first component comprises the second adhesive
portion and has a linear expansion coefficient equal to a linear
expansion coefficient of the first base plate, and the second
component comprises the second base-fixing portion and has a linear
expansion coefficient higher than the linear expansion coefficient
of the base.
9. The prism unit according to claim 8, wherein a difference
between a position of the center of the first adhesive portion and
a position of the center of the first base-fixing portion is within
.+-.5 mm.
10. The prism unit according to claim 2, wherein a difference
between a position of the center of the first adhesive portion and
a position of the center of the first base-fixing portion is within
.+-.5 mm.
11. The prism unit according to claim 2, wherein the first
base-fixing portion is formed of a bolt hole and the first base
plate is fixed to the first base plate-fixing portion of the base
by a first bolt, and the second base-fixing portion is formed of a
bolt hole and the second base plate is fixed to the second base
plate-fixing portion of the base by a second bolt.
12. The prism unit according to claim 1, wherein the first base
plate has a linear expansion coefficient equal to the linear
expansion coefficient of the first prism block.
13. The prism unit according to claim 12, wherein the second base
plate includes a first component and a second component bonded to
each other, the first component comprises the second adhesive
portion and has a linear expansion coefficient equal to a linear
expansion coefficient of the first base plate, and the second
component comprises the second base-fixing portion and has a linear
expansion coefficient higher than the linear expansion coefficient
of the base.
14. The prism unit according to claim 12, wherein a difference
between a position of the center of the first adhesive portion and
a position of the center of the first base-fixing portion is within
.+-.5 mm.
15. The prism unit according to claim 12, wherein the first
base-fixing portion is formed of a bolt hole and the first base
plate is fixed to the first base plate-fixing portion of the base
by a first bolt, and the second base-fixing portion is formed of a
bolt hole and the second base plate is fixed to the second base
plate-fixing portion of the base by a second bolt.
16. The prism unit according to claim 1, wherein the second base
plate includes a first component and a second component bonded to
each other, the first component comprises the second adhesive
portion and has a linear expansion coefficient equal to a linear
expansion coefficient of the first base plate, and the second
component comprises the second base-fixing portion and has a linear
expansion coefficient higher than the linear expansion coefficient
of the base.
17. The prism unit according to claim 16, wherein a difference
between a position of the center of the first adhesive portion and
a position of the center of the first base-fixing portion is within
.+-.5 mm.
18. The prism unit according to claim 1, wherein a difference
between a position of the center of the first adhesive portion and
a position of the center of the first base-fixing portion is within
.+-.5 mm.
19. The prism unit according to claim 1, wherein the first
base-fixing portion is formed of a bolt hole and the first base
plate is fixed to the first base plate-fixing portion of the base
by a first bolt, and the second base-fixing portion is formed of a
bolt hole and the second base plate is fixed to the second base
plate-fixing portion of the base by a second bolt.
20. The prism unit according to claim 1, wherein the composite
prism is a color separation prism or a color synthesis prism that
includes the first and second prism blocks bonded to each other so
as to form the air layer in the region including the optical axis,
and the first prism block is formed of one prism and the second
prism block is formed of two prisms bonded to each other.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a prism unit, and more
particularly, to a prism unit in which a composite prism including
a plurality of prisms bonded to each other is supported by a
base.
2. Description of the Related Art
Generally, a 3-plate type camera divides light, which has passed
through an imaging lens, into light having three colors, that is,
red (R) light, green (G) light, and blue (B) light by a color
separation prism; and receives the divided light by individual
light-receiving elements. The color separation prism is formed of a
composite prism in which a plurality of prisms are integrally
combined, is mounted on a base included in a camera body, and is
assembled to the camera body.
In the past, a color separation prism has been directly bonded to a
base and has been assembled to a camera body (see JP1995-84175A
(JP-H07-84175A)). In this case, the color separation prism has been
bonded to the base over a bonding portion between prisms.
Further, in other assembly methods, a color separation prism has
been bonded to one base plate and the base plate has been screwed
to a base and has been assembled to a camera body (see JP1997-310U
(JP-H09-310U), JP2001-42204A, and JP2008-298960A). Even in this
case, the color separation prism has been bonded and mounted on one
base plate over a bonding portion between prisms.
Furthermore, a method of supporting only one prism by bonding only
one prism to a base is also known as a method of supporting a
composite prism (see JP1989-81613U (JP-H01-81613U) and
JP1986-153124U (JP-S61-153124U)).
SUMMARY OF THE INVENTION
However, if the composite prism is bonded to the base over the
bonding portion between prisms when the composite prism is mounted
on the base, there is a drawback that the bonding portion between
the prisms is peeled due to a difference between the linear
expansion coefficient of the prism and the linear expansion
coefficient of the base when a change in temperature is received.
Particularly, since the prisms are partially bonded to each other
in a bonding portion including an air layer, there is a drawback
that a bonding force is small in the bonding portion and the
bonding portion is likely to be peeled when a change in temperature
is received. There is the same drawback even in a case in which the
composite prism is bonded to one base plate over a bonding portion
between prisms.
There is no this problem in the method of supporting only one prism
by bonding only one prism to a base, but there is a drawback that
the prism is unstably supported.
The invention has been made in consideration of these
circumstances, and an object of the invention is to provide a prism
unit that can stably support a composite prism and is strong
against a change in temperature.
Means for achieving the above-mentioned object are as follows.
(1) A prism unit comprises a composite prism that includes a first
prism block and a second prism block bonded to each other, a first
base plate that comprises a first adhesive portion and a first
base-fixing portion, a second base plate that comprises a second
adhesive portion and a second base-fixing portion, and a base that
comprises a first base plate-fixing portion and a second base
plate-fixing portion. The first prism block includes at least one
prism and the second prism block including at least one prism, the
first prism block is bonded to the first adhesive portion, the
second prism block is bonded to the second adhesive portion, and
the first base-fixing portion of the first base plate is fixed to
the first base plate-fixing portion and the second base-fixing
portion of the second base plate is fixed to the second base
plate-fixing portion. The second adhesive portion is disposed
between the first base plate-fixing portion and the second base
plate-fixing portion, and a direction in which the second base
plate-fixing portion is displaced from the first base plate-fixing
portion and a direction in which the second adhesive portion is
displaced from the second base-fixing portion are opposite to each
other in a case in which the base and the second base plate expand
or contract due to a change in temperature.
According to this aspect, the first prism block of the composite
prism is bonded to the first adhesive portion of the first base
plate and the second prism block thereof is bonded to the second
adhesive portion of the second base plate. The first base plate is
fixed to the first base plate-fixing portion, which is included in
the base, with the first base-fixing portion interposed
therebetween; and the second base plate is fixed to the second base
plate-fixing portion, which is included in the base, with the
second base-fixing portion interposed therebetween. The second
adhesive portion is disposed between the first base plate-fixing
portion and the second base plate-fixing portion so that a
direction in which the second base plate-fixing portion is
displaced from the first base plate-fixing portion and a direction
in which the second adhesive portion is displaced from the second
base-fixing portion are opposite to each other in a case in which
the base and the second base plate expand or contract due to a
change in temperature. Accordingly, since a force acting between
the first and second prism blocks can be offset when a change in
temperature is received, the peeling of the bonding portion from
the first and second prism blocks can be prevented. Further, since
the first and second prism blocks are supported, the entire
composite prism can be supported.
(2) In the prism unit according to (1), in a case in which a linear
expansion coefficient of the base is denoted by .alpha., an
equivalent linear expansion coefficient of the second base plate is
denoted by .beta., an equivalent linear expansion coefficient of
the composite prism is denoted by .gamma., a distance between the
first and second base plate-fixing portions is denoted by L mm, a
distance between the second base-fixing portion and the second
adhesive portion is denoted by M mm, and a change in the
temperature of the prism unit up to 70.degree. C. from 25.degree.
C. is denoted by .DELTA.T.degree. C., a relationship of
".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4" is satisfied.
According to this aspect, in a case in which the linear expansion
coefficient of the base is denoted by .alpha., the equivalent
linear expansion coefficient of the second base plate is denoted by
.beta., the equivalent linear expansion coefficient of the
composite prism is denoted by .gamma., the distance between the
first and second base plate-fixing portions is denoted by L mm, the
distance between the second base-fixing portion and the second
adhesive portion is denoted by M mm, and a change in the
temperature of the prism unit up to 70.degree. C. from 25.degree.
C. is denoted by .DELTA.T.degree. C., materials and the disposition
of the respective fixing portions and the respective adhesive
portions are set so as to satisfy the relationship of
".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4". Accordingly, the prism unit can
be made to have a structure that is strong against a change in
temperature.
Here, ".alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T" of
the conditions of ".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4" represents a change in the
interval of the bonding portion between the prism blocks when a
change in temperature is received. It is possible to prevent the
peeling of the bonding portion between the prism blocks, which is
caused by a change in temperature, by setting materials and the
disposition of the respective fixing portions and the respective
adhesive portions so that this change in the interval is within a
predetermined allowable range, that is, the range of
.+-.4.times.10.sup.-4 mm.
The allowable range of the change in the interval is determined
according to the bonding strength of the bonding portion between
the prism blocks, and is more preferably .+-.1.times.10.sup.-4 mm
and still more preferably .+-.5.times.10.sup.-5 mm. The bonding
strength of the bonding portion is changed according to the
viscosity or adhesive area of an adhesive to be used at the time of
bonding, and the bonding strength of the bonding portion becomes
high with an increase in the viscosity of an adhesive, and becomes
high with an increase in the adhesive area.
In a case in which the second base plate is made of a single
material, the equivalent linear expansion coefficient of the second
base plate is the linear expansion coefficient of the material. In
a case in which the second base plate is made of two or more
different materials, the equivalent linear expansion coefficient of
the second base plate is an average value of the linear expansion
coefficients of the materials. For example, in a case in which the
second base plate is made of a first material and a second
material, the equivalent linear expansion coefficient .beta. of the
second base plate is (.beta.1.times.M1+.beta.2.times.M2)/M when a
distance between the second base-fixing portion and the second
adhesive portion is denoted by M mm, the length of the first
material included therebetween is denoted by M1 mm, the length of
the second material is denoted by M2 mm, the linear expansion
coefficient of the first material is denoted by .beta.1, and the
linear expansion coefficient of the second material is denoted by
.beta.2.
As described above, in a case in which the composite prism is
formed of prisms made of a single material, the equivalent linear
expansion coefficient of the composite prism is the linear
expansion coefficient of the material. In a case in which the
composite prism is formed of prisms made of different materials,
the equivalent linear expansion coefficient of the composite prism
is a weighted average value of the linear expansion coefficients
that is obtained from the lengths of the materials in a direction
in which the extension evaluation of the linear expansion
coefficient of each of the materials is performed.
(3) In the prism unit according to (1) or (2), the first base plate
has a linear expansion coefficient equal to the linear expansion
coefficient of the first prism block.
According to this aspect, the first base plate has a linear
expansion coefficient equal to the linear expansion coefficient of
the first prism block. Accordingly, the peeling of the adhesive
portions from the first base plate and the first prism block can be
effectively prevented. "Equal" mentioned here includes a range in
which the linear expansion coefficient of the first base plate is
approximated to the linear expansion coefficient of the first prism
block other than a case in which the linear expansion coefficient
of the first base plate is completely the same as the linear
expansion coefficient of the first prism block. That is, "equal"
mentioned here includes the range of "substantially equal". In
terms of the prevention of the peeling of the adhesive portions,
the reason for this is that the peeling of the adhesive portions
can be effectively prevented if the first base plate has a linear
expansion coefficient substantially equal to the linear expansion
coefficient of the first prism block.
(4) In the prism unit according to any one of (1) to (3), the
second base plate includes a first component and a second component
bonded to each other, the first component comprises the second
adhesive portion and has a linear expansion coefficient equal to a
linear expansion coefficient of the first base plate, and the
second component comprises the second base-fixing portion and has a
linear expansion coefficient higher than the linear expansion
coefficient of the base.
According to this aspect, the second base plate includes a first
component and a second component bonded to each other, the first
component has a linear expansion coefficient equal to the linear
expansion coefficient of the first base plate, and the second
component has a linear expansion coefficient higher than the linear
expansion coefficient of the base. The first component comprises
the second adhesive portion, and the second prism block is bonded
to the first component with the second adhesive portion interposed
therebetween. Further, the second component comprises the second
base-fixing portion, and is fixed to the base with the second
base-fixing portion interposed therebetween. Accordingly, a
relationship between the height of the first adhesive portion and
the height of the second adhesive portion can be always maintained
constant even in a case in which temperature is changed. Therefore,
since the application of stress in a planar direction to the
bonding portion can be prevented, the prism unit can be made to
have a structure that is stronger against a change in temperature.
"Equal" mentioned here includes a range in which the linear
expansion coefficient of the component is approximated to the
linear expansion coefficient of the base other than a case in which
the linear expansion coefficient of the component is completely the
same as the linear expansion coefficient of the base. That is,
"equal" mentioned here includes the range of "substantially
equal".
(5) In the prism unit according to any one of (1) to (4), a
difference between the position of the center of the first adhesive
portion and the position of the center of the first base-fixing
portion is within .+-.5 mm.
According to this aspect, the difference between the position of
the center of the first adhesive portion and the position of the
center of the first base-fixing portion is set within .+-.5 mm.
That is, the first adhesive portion and the first base-fixing
portion are disposed substantially coaxially with each other.
Accordingly, an influence caused by the thermal deformation of the
first base plate can be further reduced.
(6) In the prism unit according to any one of (1) to (5), the first
base-fixing portion is formed of a bolt hole and the first base
plate is fixed to the first base plate-fixing portion of the base
by a first bolt, and the second base-fixing portion is formed of a
bolt hole and the second base plate is fixed to the second base
plate-fixing portion of the base by a second bolt.
According to this aspect, the first base-fixing portion is formed
of a bolt hole and the first base plate is fixed to the first base
plate-fixing portion of the base by the first bolt. Further, the
second base-fixing portion is formed of a bolt hole and the second
base plate is fixed to the second base plate-fixing portion of the
base by the second bolt. Accordingly, the composite prism can be
easily assembled to the base.
(7) In the prism unit according to any one of (1) to (6), in a case
in which a line passing through a center of a panel surface of an
image forming panel adjacent to the composite prism and
perpendicular to the panel surface is set as an optical axis, the
first and second prism blocks of the composite prism are bonded to
each other so as to form an air layer in a region including the
optical axis.
According to this aspect, the first and second prism blocks are
bonded to each other with an air layer interposed therebetween. In
a case in which a line passing through the center of the panel
surface of the image forming panel adjacent to the composite prism
and perpendicular to the panel surface is set as an optical axis,
the air layer is formed in a region including the optical axis.
Since the bonding strength of the bonding portion deteriorates when
the air layer is formed in the bonding portion, the invention more
effectively acts.
(8) In the prism unit according to (7), the composite prism is a
color separation prism or a color synthesis prism that includes the
first and second prism blocks bonded to each other so as to form an
air layer in a region including the optical axis, and the first
prism block is formed of one prism and the second prism block is
formed of two prisms bonded to each other.
According to this aspect, the composite prism forms a color
separation prism or a color synthesis prism. In this case, the
composite prism is built in, for example, a 3-plate type camera and
can be used to separate the color of incident light.
(9) In the prism unit according to (7) or (8), the first and second
prism blocks of the composite prism are bonded to each other with a
spacer interposed therebetween in a region other than the region
including the optical axis.
According to this aspect, the first and second prism blocks are
bonded to each other with a spacer interposed therebetween in a
region other than the region including the optical axis.
Accordingly, an air layer having a constant thickness can be easily
formed in the bonding portion.
According to the invention, a prism unit can stably support a
composite prism and can be made to have a structure strong against
a change in temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view showing the schematic structure of a 3-plate
type camera in which a prism unit according to the invention is
built.
FIG. 2 is a plan view showing the schematic structure of the
3-plate type camera in which the prism unit according to the
invention is built.
FIG. 3 is a cross-sectional view taken along line 3-3 of FIG.
2.
FIG. 4 is a cross-sectional view of a bonding portion between a
first prism block and a second prism block.
FIG. 5 is a plan view of a first base plate and a second base plate
that are mounted on a base.
FIG. 6 is a side cross-sectional view showing the schematic
structure of a second embodiment of the 3-plate type camera in
which the prism unit according to the invention is built.
FIG. 7 is a plan view of first and second base plates that are
mounted on the base.
FIG. 8 is a plan view showing the schematic structure of a
projection display device in which the prism unit according to the
invention is built.
FIG. 9 is a plan view of the prism unit.
FIG. 10 is a cross-sectional view taken along line 10-10 of FIG.
9.
FIGS. 11A and 11B are views showing other embodiments of a
spacer.
FIG. 12 is a table showing results of verification experiments
about effects.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the invention will be described in detail
below with reference to accompanying drawings.
First Embodiment
<Structure>
FIG. 1 is a side view showing the schematic structure of a 3-plate
type camera in which a prism unit according to the invention is
built, and FIG. 2 is a plan view showing the schematic structure of
the 3-plate type camera in which the prism unit according to the
invention is built. Further, FIG. 3 is a cross-sectional view taken
along line 3-3 of FIG. 2.
The 3-plate type camera 1 separates light, which has passed through
an imaging lens (not shown), into light having three colors, that
is, red (R) light, green (G) light, and blue (B) light; and
receives the red (R) light, the green (G) light, and the blue (B)
light by three imaging elements 3R, 3G, and 3B, respectively. The
imaging lens is mounted on a lens mount 4 that is included in a
camera body 2. A prism unit 10 functions as color separation means
for dividing the light, which has passed through the imaging lens,
into light having three colors, that is, red (R) light, green (G)
light, and blue (B) light.
The prism unit 10 mainly includes a color separation prism 12, a
base 14 that supports the color separation prism 12, and a first
base plate 16 and a second base plate 18 that are used to mount the
color separation prism 12 on the base 14.
[Color separation prism]
The color separation prism 12 is a composite prism, and includes a
plurality of prisms that are made of glass and are bonded to each
other. The color separation prism 12 of this embodiment includes a
first prism block 20 and a second prism block 22 that are bonded to
each other.
The first prism block 20 includes one prism. The first prism block
20 includes an imaging light-incident surface 20a, a blue
light-reflecting surface 20b, and a blue light-emitting surface
20c.
The imaging light-incident surface 20a is disposed perpendicular to
an optical axis OL of the imaging lens. Light, which has passed
through the imaging lens, is incident on the imaging light-incident
surface 20a.
The blue light-reflecting surface 20b includes a dichroic film that
reflects only blue light. Only blue light of the light, which is
incident from the imaging light-incident surface 20a, is reflected
by the blue light-reflecting surface 20b and the rest thereof is
transmitted through the blue light-reflecting surface 20b.
The blue light, which is reflected by the blue light-reflecting
surface 20b, is totally reflected by the imaging light-incident
surface 20a, and is emitted from the blue light-emitting surface
20c. The blue light, which is emitted from the blue light-emitting
surface 20c, is received by a light-receiving surface 3b of an
imaging element 3B that receives blue light.
The second prism block 22 includes two prisms 22A and 22B that are
integrally bonded to each other. The second prism block 22 includes
an incident surface 22a, a red light-reflecting surface 22b, a red
light-emitting surface 22c, and a green light-emitting surface
22d.
The incident surface 22a is disposed so as to face the blue
light-reflecting surface 20b of the first prism block 20 with a
constant interval therebetween. The light, which has been
transmitted through the blue light-reflecting surface 20b of the
first prism block 20, is incident on the incident surface 22a of
the second prism block 22.
The red light-reflecting surface 22b is formed of a bonding surface
between the two prisms 22A and 22B of the second prism block 22.
Bonding of the two prisms 22A and 22B is gapless bonding, and the
bonding surfaces of the prisms 22A and 22B are bonded to each other
without a gap. A dichroic film, which reflects only red light, is
provided on the bonding surface of one prism 22A of the two prisms
22A and 22B. Only red light of the light, which is incident on the
incident surface 22a, is reflected by the red light-reflecting
surface 22b and the rest thereof is transmitted through the red
light-reflecting surface 22b.
The red light, which is reflected by the red light-reflecting
surface 22b, is totally reflected by the incident surface 22a, and
is emitted from the red light-emitting surface 22c. The red light,
which is emitted from the red light-emitting surface 22c, is
received by a light-receiving surface 3r of an imaging element 3R
that receives red light.
The light, which has been transmitted through the red
light-reflecting surface 22b, is emitted from the green
light-emitting surface 22d as green light. The green light, which
is emitted from the green light-emitting surface 22d, is received
by a light-receiving surface 3g of an imaging element 3G that
receives green light.
An air layer 24 is provided between the blue light-reflecting
surface 20b of the first prism block 20 and the incident surface
22a of the second prism block 22. The air layer 24 is provided to
totally reflect the light that is reflected by the red
light-reflecting surface 22b of the second prism block 22.
In a case in which a line passing through the centers of the
light-receiving surfaces 3r, 3b, and 3g of the adjacent imaging
elements 3R, 3G, and 3B and perpendicular to the light-receiving
surfaces 3r, 3g, and 3b is referred to as an optical axis OP, the
first and second prism blocks 20 and 22 are bonded to each other so
that the air layer 24 is formed in a region including the optical
axis OP. The first and second prism blocks 20 and 22 are bonded to
each other with a spacer 26 interposed therebetween.
FIG. 4 is a cross-sectional view of a bonding portion between the
first prism block and the second prism block, and is a
cross-sectional view taken along line 4-4 of FIG. 2. As shown in
FIG. 4, the spacer 26 has the shape of a frame having a constant
thickness and is disposed in a region other than a region including
the optical axis OP. Accordingly, the first and second prism blocks
20 and 22 are bonded to each other so that the air layer 24 is
formed in the region including the optical axis OP. An adhesive is
applied to both surfaces of the spacer 26 so as to have a constant
thickness and the spacer 26 is adhered to the blue light-reflecting
surface 20b of the first prism block 20 and the incident surface
22a of the second prism block 22, so that the first and second
prism blocks 20 and 22 are bonded to each other.
Since the blue light-reflecting surface 20b of the first prism
block 20 and the incident surface 22a of the second prism block 22
are bonded to each other with the spacer 26 interposed
therebetween, the first and second prism blocks 20 and 22 are
integrated with each other. As a result, one color separation prism
12 is formed.
Each of the imaging elements 3R, 3G, and 3B is an example of an
image forming panel, and is mounted on the color separation prism
12 by a holder (not shown). Each of the imaging elements 3R, 3G,
and 3B is disposed so as to face the corresponding emitting
surface, and is disposed so that light passing through the optical
axis of the imaging lens is incident on the centers of the
light-receiving surfaces 3r, 3g, and 3b as the surfaces of the
panels so as to be perpendicular to the light-receiving surfaces
3r, 3g, and 3b. Each of the imaging elements 3R, 3G, and 3B is
formed of, for example, an image sensor, such as a charged coupled
device (CCD) or a complementary metal oxide semiconductor
(CMOS).
[Base]
As shown in FIGS. 1 to 3, the base 14 is mounted on the camera body
2 and functions as a member that supports the color separation
prism 12 in the camera body 2. The base 14 has an L shape, and
includes a leg portion 14A and a prism support portion 14B.
The leg portion 14A is a portion that is used to fix the base 14 to
the camera body 2. The leg portion 14A includes a bolt insertion
hole 14a. The bolt insertion hole 14a is formed of a through hole,
and is provided in parallel to the prism support portion 14B. A
base fixing bolt 28 is inserted into the bolt insertion hole 14a,
so that the base 14 is bolted to the camera body 2. The camera body
2 includes bolt holes 2A that are used to bolt the base 14.
The prism support portion 14B is a portion that is used to support
the color separation prism 12. The prism support portion 14B has
the shape of a rectangular flat plate.
When the leg portion 14A of the base 14 is bolted to the camera
body 2, the support portion 14B is disposed in parallel to the
optical axis OL of the imaging lens.
[First Base Plate and Second Base Plate]
The first and second base plates 16 and 18 are members that are
used to mount the color separation prism 12 on the base 14. The
first base plate 16 is mounted on the first prism block 20 of the
color separation prism 12. The second base plate 18 is mounted on
the second prism block 22 of the color separation prism 12.
FIG. 5 is a plan view of the first and second base plates that are
mounted on the base.
The first base plate 16 has the shape of a flat plate, and includes
a flat first prism-adhesive surface 16a and a flat first
base-fixing surface 16b. The first base plate 16 has an outer shape
substantially corresponding to the shape of a base
plate-installation surface 20S of the first prism block 20.
The second base plate 18 has the shape of a flat plate having the
same thickness as the first base plate 16, and includes a flat
second prism-adhesive surface 18a and a flat second base-fixing
surface 18b. The second base plate 18 has an outer shape
substantially corresponding to the shape of a base
plate-installation surface 22S of the second prism block 22.
A first adhesive portion 16A, which is used to mount the first
prism block 20 of the color separation prism 12, is provided on the
first prism-adhesive surface 16a of the first base plate 16. The
first adhesive portion 16A is formed as a portion to which an
adhesive is to be applied. An adhesive is applied to the first
adhesive portion 16A of the first base plate 16 so as to have a
constant thickness, and the first base plate 16 is mounted on the
base plate-installation surface 20S of the first prism block 20.
Accordingly, the first prism block 20 and the first base plate 16
are integrated with each other.
A second adhesive portion 18A, which is used to mount the second
prism block 22 of the color separation prism 12, is provided on the
second prism-adhesive surface 18a of the second base plate 18. The
second adhesive portion 18A is formed as a portion to which an
adhesive is to be applied. An adhesive is applied to the second
adhesive portion 18A of the second base plate 18 so as to have a
constant thickness, and the second base plate 18 is mounted on the
base plate-installation surface 22S of the second prism block 22.
Accordingly, the second prism block 22 and the second base plate 18
are integrated with each other.
The first and second base plates 16 and 18, which are mounted on
the color separation prism 12, are mounted on the color separation
prism 12 with a constant gap therebetween.
A first base-fixing portion 16B, which is used to mount the first
base plate 16 on the base 14, is provided on the first base-fixing
surface 16b of the first base plate 16. The first base-fixing
portion 16B is formed of a bolt hole.
A second base-fixing portion 18B, which is used to mount the second
base plate 18 on the base 14, is provided on the second base-fixing
surface 18b of the second base plate 18. The second base-fixing
portion 18B is formed of a bolt hole.
The base 14 includes a first base plate-fixing portion 14C that is
used to mount the first base plate 16 and a second base
plate-fixing portion 14D that is used to mount the second base
plate 18. The first and second base plate-fixing portions 14C and
14D are provided in the prism support portion 14B of the base 14,
and are formed of through holes, respectively. A first bolt 30 is
inserted into the first base plate-fixing portion 14C and is
screwed to the first base-fixing portion 16B, so that the first
base plate 16 is fixed to the base 14. Further, a second bolt 32 is
inserted into the second base plate-fixing portion 14D and is
screwed to the second base-fixing portion 18B, so that the second
base plate 18 is fixed to the base 14.
[Disposition of Respective Portions]
When the base 14 is mounted on the camera body 2, the first and
second base plate-fixing portions 14C and 14D are disposed on a
straight line parallel to the optical axis OL of the imaging
lens.
Further, the first base-fixing portion 16B, the second base-fixing
portion 18B, the first adhesive portion 16A, and the second
adhesive portion 18A are disposed on the same straight line, and
are disposed on a straight line passing through the center of the
first base plate-fixing portion 14C and the center of the second
base plate-fixing portion 14D when the first and second base plates
16 and 18 are mounted on the base 14.
Accordingly, when the base 14 is mounted on the camera body 2, the
respective portions, that is, all of the first base plate-fixing
portion 14C, the second base plate-fixing portion 14D, the first
base-fixing portion 16B, the second base-fixing portion 18B, the
first adhesive portion 16A, and the second adhesive portion 18A are
disposed on one straight line parallel to the optical axis OL of
the imaging lens.
Furthermore, the first adhesive portion 16A is disposed coaxially
with the first base-fixing portion 16B. Accordingly, when the first
base plate 16 is mounted on the base 14, the first adhesive portion
16A, the first base-fixing portion 16B, and the first base
plate-fixing portion 14C are disposed coaxially with each other.
Since the first adhesive portion 16A and the first base-fixing
portion 16B are disposed coaxially with each other in this way, it
is possible to reduce an influence that is caused by the thermal
deformation of the first base plate 16. A range in which it is
regarded that elements are disposed coaxially with each other
includes a fixed allowable range, and includes a range in which it
is regarded that elements are disposed substantially coaxially with
each other. This range is set to a range in which a difference
between the position of the center of the first adhesive portion
16A and the position of the center of the first base-fixing portion
16B is within .+-.5 mm. In this range, it can be regarded that
elements are disposed substantially coaxially with each other and
an influence caused by the thermal deformation of the first base
plate 16 can be further reduced.
Further, the second adhesive portion 18A is disposed between the
first base plate-fixing portion 14C and the second base
plate-fixing portion 14D. Accordingly, a direction in which the
second base plate-fixing portion 14D is displaced from the first
base plate-fixing portion 14C and a direction in which the second
adhesive portion 18A is displaced from the second base-fixing
portion 18B are opposite to each other in a case in which the base
14 and the second base plate 18 expand or contract due to a change
in temperature. Therefore, since an increase and a reduction in the
interval of the bonding portion between the first and second prism
blocks 20 and 22 of the color separation prism 12, which are caused
by a change in temperature, can be suppressed, the peeling of the
bonding portion can be prevented.
Particularly, the prism unit 10 of this embodiment is adapted to
satisfy the following conditions. That is, in a case in which the
linear expansion coefficient of the base 14 is denoted by .alpha.,
the equivalent linear expansion coefficient of the second base
plate 18 is denoted by .beta., the equivalent linear expansion
coefficient of the color separation prism 12 as a composite prism
is denoted by .gamma., a distance between the first and second base
plate-fixing portions 14C and 14D is denoted by L mm, a distance
between the second base-fixing portion 18B and the second adhesive
portion 18A is denoted by M mm, and a change in the temperature of
the prism unit 10 up to 70.degree. C. from 25.degree. C. is denoted
by .DELTA.T.degree. C. as shown in FIG. 3, the prism unit 10 of
this embodiment is adapted to satisfy the relationship of
".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4". Accordingly, since an increase
and a reduction in the interval of the bonding portion, which are
caused by a change in temperature, can be more appropriately
suppressed, the peeling of the bonding portion can be
prevented.
Here, ".alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T" of
the conditions of ".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4" represents a change in the
interval of the bonding portion between the first and second prism
blocks 20 and 22 when a change in temperature is received. It is
possible to prevent the peeling of the bonding portion between the
first and second prism blocks 20 and 22, which is caused by a
change in temperature, by setting materials and the disposition of
the respective fixing portions and the respective adhesive portions
so that this change in the interval is within a predetermined
allowable range, that is, the range of .+-.4.times.10.sup.-4
mm.
The allowable range of the change in the interval is determined
according to the bonding strength of the bonding portion between
the first and second prism blocks 20 and 22, and is more preferably
.+-.1.times.10.sup.-4 mm and still more preferably
.+-.5.times.10.sup.-5 mm. The bonding strength of the bonding
portion is changed according to the viscosity or adhesive area of
an adhesive to be used at the time of bonding, and the bonding
strength of the bonding portion becomes high with an increase in
the viscosity of an adhesive, and becomes high with an increase in
the adhesive area.
Here, in order to satisfy the conditions of ".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4", the materials of the base 14 and
the first and second base plates 16 and 18 are appropriately
selected other than the adjustment of the disposition of the
respective portions, that is, the first base plate-fixing portion
14C, the second base plate-fixing portion 14D, the first
base-fixing portion 16B, the second base-fixing portion 18B, the
first adhesive portion 16A, and the second adhesive portion
18A.
The base 14 can be made of, for example, an aluminum alloy. It is
preferable that the first base plate 16 is made of a material
having a linear expansion coefficient equal to the equivalent
linear expansion coefficient of the color separation prism 12.
Accordingly, the peeling of the adhesive portions from the color
separation prism 12 can be effectively prevented. "Equal" mentioned
here includes a range in which the linear expansion coefficient is
approximated to the equivalent linear expansion coefficient other
than a case in which the linear expansion coefficient is completely
the same as the equivalent linear expansion coefficient. That is,
"equal" mentioned here includes the range of "substantially equal".
In terms of the prevention of the peeling of the adhesive portions,
the reason for this is that the peeling of the adhesive portions
can be effectively prevented if the first base plate 16 has a
linear expansion coefficient substantially equal to the equivalent
linear expansion coefficient of the color separation prism 12. In
the case of the color separation prism made of glass, the first
base plate 16 can be made of, for example, ceramics or titanium.
Further, the camera body 2 can be made of, for example, an aluminum
alloy.
In a case in which the second base plate 18 is made of a single
material, the equivalent linear expansion coefficient of the second
base plate 18 is the linear expansion coefficient of the material.
In a case in which the second base plate 18 is made of two or more
different materials, the equivalent linear expansion coefficient of
the second base plate 18 is an average value of the linear
expansion coefficients of the materials. Since the second base
plate 18 is made of a single material in this embodiment, the
equivalent linear expansion coefficient of the second base plate 18
is the linear expansion coefficient of the material of the second
base plate 18.
Likewise, in a case in which the color separation prism 12 is
formed of a prism made of a single material, the equivalent linear
expansion coefficient .gamma. of the color separation prism 12 as a
composite prism is the linear expansion coefficient of the
material. In a case in which the color separation prism 12 is
formed of a prism made of different materials, the equivalent
linear expansion coefficient .gamma. of the color separation prism
12 is an average value of the linear expansion coefficients of the
materials. Since each prism forming the color separation prism 12
is made of a single material (glass) in this embodiment, the
equivalent linear expansion coefficient .gamma. is the linear
expansion coefficient of the prism forming the color separation
prism 12. In this case, the equivalent linear expansion coefficient
of the first prism block 20 and the equivalent linear expansion
coefficient of the second prism block 22 are also the linear
expansion coefficient of the material of the prism.
<Action>
When the color separation prism 12 is mounted on the base 14 with
the first and second base plates 16 and 18 interposed therebetween
and the base 14 is assembled to the camera body 2 as shown in FIGS.
1 to 3, the color separation prism 12 is disposed on the optical
axis OL of the imaging lens. Accordingly, the imaging element 3G
receiving green light is disposed on the optical axis OL of the
imaging lens.
Light, which has been transmitted through the imaging lens, is
incident on the imaging light-incident surface 20a of the color
separation prism 12. The light, which is incident on the imaging
light-incident surface 20a, is divided into light having three
colors, that is, red (R) light, green (G) light, and blue (B) light
in the color separation prism 12. Further, the red light is emitted
from the red light-emitting surface 22c and is received by the
light-receiving surface 3r of the imaging element 3R receiving red
light, the green light is emitted from the green light-emitting
surface 22d and is received by the light-receiving surface 3g of
the imaging element 3G receiving green light, and the blue light is
emitted from the blue light-emitting surface 20c and is received by
the light-receiving surface 3b of the imaging element 3B receiving
blue light. Accordingly, the optical image of a subject, which has
passed through the imaging lens, is taken.
Incidentally, when a power source is turned on, various devices
installed in the camera body 2 of the 3-plate type camera 1
generate heat and the internal temperature of the camera body 2
rises. When the internal temperature of the camera body 2 rises,
the base 14, which is a support portion for the color separation
prism 12, and the first and second base plates 16 and 18 are
thermally deformed. When the base 14 and the first and second base
plates 16 and 18 are thermally deformed, the prism unit 10 of this
embodiment acts as follows.
That is, when the base 14 expands due to a temperature rise, the
second base plate-fixing portion 14D is displaced in a direction in
which the second base plate-fixing portion 14D becomes distant from
the first base plate-fixing portion 14C. As a result, the second
adhesive portion 18A is displaced in a direction in which the
second adhesive portion 18A becomes distant from the first adhesive
portion 16A.
On the other hand, when the second base plate 18 expands due to a
temperature rise, the second adhesive portion 18A is displaced in a
direction in which the second adhesive portion 18A becomes distant
from the second base plate-fixing portion 14D. This direction is a
direction opposite to a direction in which the second adhesive
portion 18A is displaced due to the expansion of the base 14, and
is a direction approaching the first adhesive portion 16A.
That is, since the second base plate 18 is displaced so as to
offset the displacement of the base 14 when temperature is changed,
an interval between the first and second adhesive portions 16A and
18A can be always maintained constant. Accordingly, since a force
acting between the first and second prism blocks 20 and 22 of the
color separation prism 12 can be offset, the peeling of the bonding
portion from the first and second prism blocks 20 and 22 can be
prevented.
Further, since both the first and second prism blocks 20 and 22 are
supported in the prism unit 10 of this embodiment, the color
separation prism 12 can be supported in a stable state.
Furthermore, since the first and second adhesive portions 16A and
18A are disposed close to each other in the prism unit 10 of this
embodiment, an influence of thermal expansion can be minimized.
Second Embodiment
<Structure>
FIG. 6 is a side cross-sectional view showing the schematic
structure of a second embodiment of the 3-plate type camera in
which the prism unit according to the invention is built. Further,
FIG. 7 is a plan view of first and second base plates that are
mounted on the base.
As shown in FIGS. 6 and 7, the second base plate 18 of a prism unit
10A of this embodiment includes a first component 18C and a second
component 18D that are bonded to each other. The structure of the
prism unit 10A of this embodiment is the same as the structure of
the prism unit 10 of the first embodiment except that the structure
of the second base plate 18 is different from that of the second
base plate 18 of the first embodiment. Accordingly, only the
structure of the second base plate 18 and the functional effects
thereof will be described here.
As described above, the second base plate 18 of the prism unit 10A
of this embodiment includes the first and second components 18C and
18D that are bonded to each other.
The first component 18C includes a second adhesive portion 18A, and
has a linear expansion coefficient equal to the linear expansion
coefficient of the first base plate 16. Further, the first
component 18C has the same thickness as the first base plate 16.
"Equal" mentioned here includes a range in which the linear
expansion coefficient is approximated to the equivalent linear
expansion coefficient other than a case in which the linear
expansion coefficient is completely the same as the equivalent
linear expansion coefficient. That is, "equal" mentioned here
includes the range of "substantially equal". Likewise, "the same
thickness" includes "substantially the same thickness".
The second component 18D includes a second base-fixing portion 18B,
and has a linear expansion coefficient higher than the linear
expansion coefficient of the base 14. The second component 18D has
a thickness slightly larger than the thickness of the first
component 18C.
The first and second components 18C and 18D are integrated with
each other by being bonded to each other by, for example, an
adhesive. The second base plate 18 of which the first and second
components 18C and 18D are integrated with each other has an outer
shape substantially corresponding to the shape of the base
plate-installation surface 22S of the second prism block 22.
<Action>
According to the prism unit 10A of this embodiment, a relationship
between the height of the first adhesive portion 16A and the height
of the second adhesive portion 18A can be always maintained
constant even in a case in which temperature is changed.
The first and second base plates 16 and 18 also expand in a
thickness direction due to a change in temperature, but it is
possible to make the deformation amount of the first component 18C
and the deformation amount of the first base plate 16, which are
caused by thermal expansion, correspond to each other by making the
linear expansion coefficient of the first component 18C of the
second base plate 18 correspond to the linear expansion coefficient
of the first base plate 16. Accordingly, even in a case in which
temperature is changed, the height of the first adhesive portion
16A can be always the same as the height of the second adhesive
portion 18A.
Further, since the height of the first adhesive portion 16A can be
always the same as the height of the second adhesive portion 18A,
it is possible to prevent stress, which is applied in a direction
along the bonding surface, from being applied to the bonding
portion of the color separation prism 12. Accordingly, the prism
unit can be made to have a structure that is stronger against a
change in temperature.
In a case in which the color separation prism 12 is made of glass,
the first base plate 16 and the first component 18C of the second
base plate 18 can be made of, for example, ceramics or titanium.
Accordingly, the peeling of the adhesive portion between the first
prism block 20 and the first base plate 16 can be effectively
prevented. Further, the peeling of the adhesive portion between the
second prism block 22 and the second base plate 18 can be
effectively prevented.
Third Embodiment
<Structure>
FIG. 8 is a plan view showing the schematic structure of a
projection display device in which the prism unit according to the
invention is built.
The projection display device 100 shown in FIG. 8 is a projection
display device using a reflective light valve, and mainly includes
a light source 101, a relay lens 102, a total reflection mirror
103, a field lens 104, a total reflection prism 112, a reflective
light valve 105, and a projection lens 106.
Light, which is emitted from the light source 101, is incident on
the total reflection mirror 103 through the relay lens 102. Then,
the light is totally reflected by the total reflection mirror 103,
and is incident on the total reflection prism 112 through the field
lens 104.
The total reflection prism 112 is formed of a composite prism, and
includes a first prism block 120 and a second prism block 122 that
are bonded to each other. The first prism block 120 is formed of a
prism as a single body, and the second prism block 122 is formed of
a prism as a single body likewise. The first and second prism
blocks 120 and 122 are bonded to each other with an air layer
interposed therebetween. The light, which is incident on the total
reflection prism 112, is totally reflected by the interface of the
air layer and is incident on the reflective light valve 105.
The reflective light valve 105 is an example of an image forming
panel, and controls the traveling direction of light to be incident
on an image forming surface as the surface of the panel and forms
an optical image.
Light, which is reflected from the reflective light valve 105, is
incident on the projection lens 106 after being transmitted through
the total reflection prism 112, and is applied to a screen.
Accordingly, the optical image formed on the reflective light valve
105 is enlarged and projected to the screen.
FIG. 9 is a plan view of the prism unit. Further, FIG. 10 is a
cross-sectional view taken along line 10-10 of FIG. 9.
The total reflection prism 112 is assembled to a device body 107 of
the projection display device 100 as a prism unit 110.
The prism unit 110 includes the total reflection prism 112, a base
114 that supports the total reflection prism 112, and a first base
plate 116 and a second base plate 118 that are used to mount the
total reflection prism 112 on the base 114.
[Total Reflection Prism]
As described above, the total reflection prism 112 is a composite
prism and includes the first and second prism blocks 120 and 122
that are bonded to each other.
In a case in which a line passing through the center of the image
forming surface of the reflective light valve 105 and perpendicular
to the image forming surface is set as an optical axis OP, the
first and second prism blocks 120 and 122 are bonded to each other
so that an air layer 124 is formed in a region including the
optical axis. The first and second prism blocks 120 and 122 are
bonded to each other with a spacer 126 interposed therebetween. The
spacer 126 has the shape of a frame, and is disposed in a region
other than the region including the optical axis OP.
[Base]
The base 114 functions as a member that supports the total
reflection prism 112 in the device body 107. The base 114 includes
a pair of leg portions 114A and a prism support portion 114B.
The pair of leg portions 114A is a portion that is used to fix the
base 114 to the device body 107. Each of the leg portions 114A has
an L shape, and includes a bolt insertion hole 114a formed of a
through hole. A base fixing bolt 128 is inserted into each bolt
insertion hole 114a, so that the base 114 is bolted to the device
body 107. The device body 107 includes a pair of bolt holes 107A
that is used to bolt the base 114.
The prism support portion 114B is a portion that supports the total
reflection prism 112. The prism support portion 114B has the shape
of a rectangular flat plate.
When the leg portions 114A are bolted to the device body 107, the
base 114 is disposed so that the prism support portion 114B is
parallel to an optical axis OL of the projection lens 106. The
optical axis OL of the projection lens 106 and the optical axis OP
correspond to each other. That is, the reflective light valve 105
is installed on the optical axis of the projection lens 106.
[First Base Plate and Second Base Plate]
The first and second base plates 116 and 118 are members that are
used to mount the total reflection prism 112 on the base 114. The
first base plate 116 is mounted on the first prism block 120 of the
total reflection prism 112. The second base plate 118 is mounted on
the second prism block 122 of the total reflection prism 112.
FIG. 9 is a plan view of the first and second base plates mounted
on the base.
The first base plate 116 has the shape of a flat plate, and
includes a flat first prism-adhesive surface 116a and a flat first
base-fixing surface 116b.
The second base plate 118 has the shape of a flat plate having the
same thickness as the first base plate 116, and includes a flat
second prism-adhesive surface 118a and a flat second base-fixing
surface 118b.
A first adhesive portion 116A, which is used to mount the first
prism block 120 of the total reflection prism 112, is provided on
the first prism-adhesive surface 116a of the first base plate 116.
The first adhesive portion 116A is formed as a portion to which an
adhesive is to be applied. An adhesive is applied to the first
adhesive portion 116A of the first base plate 116 so as to have a
constant thickness, and the first base plate 116 is mounted on a
base plate-installation surface 120S of the first prism block 120.
Accordingly, the first prism block 120 and the first base plate 116
are integrated with each other.
A second adhesive portion 118A, which is used to mount the second
prism block 122 of the total reflection prism 112, is provided on
the second prism-adhesive surface 118a of the second base plate
118. The second adhesive portion 118A is formed as a portion to
which an adhesive is to be applied. An adhesive is applied to the
second adhesive portion 118A of the second base plate 118 so as to
have a constant thickness, and the second base plate 118 is mounted
on a base plate 122S of the second prism block 122. Accordingly,
the second prism block 122 and the second base plate 118 are
integrated with each other.
The first and second base plates 116 and 118, which are mounted on
the total reflection prism 112, are mounted on the total reflection
prism 112 with a constant gap therebetween.
A first base-fixing portion 116B, which is used to mount the first
base plate 116 on the base 114, is provided on the first
base-fixing surface 116b of the first base plate 116. The first
base-fixing portion 116B is formed of a bolt hole.
A second base-fixing portion 118B, which is used to mount the
second base plate 118 on the base 114, is provided on the second
base-fixing surface 118b of the second base plate 118. The second
base-fixing portion 118B is formed of a bolt hole.
The base 114 includes a first base plate-fixing portion 114C that
is used to mount the first base plate 116 and a second base
plate-fixing portion 114D that is used to mount the second base
plate 118. The first and second base plate-fixing portions 114C and
114D are provided in the prism support portion 14B of the base 114,
and are formed of through holes, respectively. A first bolt 130 is
inserted into the first base plate-fixing portion 114C and is
screwed to the first base-fixing portion 116B, so that the first
base plate 116 is fixed to the base 114. Further, a second bolt 132
is inserted into the second base plate-fixing portion 114D and is
screwed to the second base-fixing portion 118B, so that the second
base plate 118 is fixed to the base 114.
[Disposition of Respective Portions]
When the base 114 is mounted on the device body 107, the first and
second base plate-fixing portions 114C and 114D are disposed on a
straight line parallel to the optical axis OL of the projection
lens 106.
Further, the first base-fixing portion 116B, the second base-fixing
portion 118B, the first adhesive portion 116A, and the second
adhesive portion 118A are disposed on the same straight line, and
are disposed on a straight line passing through the center of the
first base plate-fixing portion 114C and the center of the second
base plate-fixing portion 114D when the first and second base
plates 116 and 118 are mounted on the base 114.
Accordingly, when the base 114 is mounted on the device body 107,
the respective portions, that is, all of the first base
plate-fixing portion 114C, the second base plate-fixing portion
114D, the first base-fixing portion 116B, the second base-fixing
portion 118B, the first adhesive portion 116A, and the second
adhesive portion 118A are disposed on one straight line parallel to
the optical axis OL of the projection lens 106.
Furthermore, the first adhesive portion 116A is disposed coaxially
with the first base-fixing portion 116B. Accordingly, when the
first base plate 116 is mounted on the base 114, the first adhesive
portion 116A, the first base-fixing portion 116B, and the first
base plate-fixing portion 114C are disposed coaxially with each
other.
Further, the second adhesive portion 118A is disposed between the
first base plate-fixing portion 114C and the second base
plate-fixing portion 114D. Accordingly, a direction in which the
second base plate-fixing portion 114D is displaced from the first
base plate-fixing portion 114C and a direction in which the second
adhesive portion 118A is displaced from the second base-fixing
portion 118B are opposite to each other in a case in which the base
114 and the second base plate 118 expand or contract due to a
change in temperature. Therefore, since an increase and a reduction
in the interval of the bonding portion between the first and second
prism blocks 120 and 122 of the total reflection prism 112, which
are caused by a change in temperature, can be suppressed, the
peeling of the bonding portion can be prevented.
Particularly, the prism unit 110 of this embodiment is adapted to
satisfy the following conditions. That is, in a case in which the
linear expansion coefficient of the base 114 is denoted by .alpha.,
the equivalent linear expansion coefficient of the total reflection
prism 112 as a composite prism is denoted by .gamma., the
equivalent linear expansion coefficient of the second base plate
118 is denoted by .beta., a distance between the first and second
base plate-fixing portions 114C and 114D is denoted by L mm, a
distance between the second base-fixing portion 118B and the second
adhesive portion 118A is denoted by M mm, and a change in the
temperature of the prism unit 110 up to 70.degree. C. from
25.degree. C. is denoted by .DELTA.T.degree. C. as shown in FIG. 3,
the prism unit 110 of this embodiment is adapted to satisfy the
relationship of ".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4". Accordingly, since an increase
and a reduction in the interval of the bonding portion, which are
caused by a change in temperature, can be more appropriately
suppressed, the peeling of the bonding portion can be
prevented.
Here, ".alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T" of
the conditions of ".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4" represents a change in the
interval of the bonding portion between the first and second prism
blocks 120 and 122 when a change in temperature is received. It is
possible to prevent the peeling of the bonding portion between the
first and second prism blocks 120 and 122, which is caused by a
change in temperature, by setting materials and the disposition of
the respective fixing portions and the respective adhesive portions
so that this change in the interval is within a predetermined
allowable range, that is, the range of .+-.4.times.10.sup.-4.
The allowable range of the change in the interval is determined
according to the bonding strength of the bonding portion between
the first and second prism blocks 120 and 122, and is more
preferably .+-.1.times.10.sup.-4 and still more preferably
.+-.5.times.10.sup.-5. The bonding strength of the bonding portion
is changed according to the viscosity or adhesive area of an
adhesive to be used at the time of bonding, and the bonding
strength of the bonding portion becomes high with an increase in
the viscosity of an adhesive, and becomes high with an increase in
the adhesive area.
In order to satisfy the conditions of ".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4", the materials of the base 114 and
the first and second base plates 116 and 118 are appropriately
selected other than the adjustment of the disposition of the
respective portions, that is, the first base plate-fixing portion
114C, the second base plate-fixing portion 114D, the first
base-fixing portion 116B, the second base-fixing portion 118B, the
first adhesive portion 116A, and the second adhesive portion
118A.
The base 114 can be made of, for example, an aluminum alloy. It is
preferable that the first and second base plate 116 and 118 are
made of a material having a linear expansion coefficient equal to
the linear expansion coefficient of the total reflection prism 112.
Accordingly, the peeling of the adhesive portions from the total
reflection prism 112 can be effectively prevented. "Equal"
mentioned here includes a range in which the linear expansion
coefficient of the material of each of the first and second base
plate 116 and 118 is approximated to the linear expansion
coefficient of the total reflection prism 112 other than a case in
which the linear expansion coefficient of the material of each of
the first and second base plate 116 and 118 is completely the same
as the linear expansion coefficient of the total reflection prism
112. That is, "equal" mentioned here includes the range of
"substantially equal". In terms of the prevention of the peeling of
the adhesive portions, the reason for this is that the peeling of
the adhesive portions can be effectively prevented if the first and
second base plate 116 and 118 have a linear expansion coefficient
substantially equal to the linear expansion coefficient of the
total reflection prism 112. In the case of the total reflection
prism made of glass, the first and second base plate 116 and 118
can be made of, for example, ceramics or titanium. Further, the
device body 107 can be made of, for example, an aluminum alloy.
<Action>
When the base 114 and the first and second base plates 116 and 118
are thermally deformed, the prism unit 110 acts as follows. That
is, when the base 114 expands due to a temperature rise, the second
base plate-fixing portion 114D is displaced in a direction in which
the second base plate-fixing portion 114D becomes distant from the
first base plate-fixing portion 114C. As a result, the second
adhesive portion 118A is displaced in a direction in which the
second adhesive portion 118A becomes distant from the first
adhesive portion 116A. On the other hand, when the second base
plate 118 expands due to a temperature rise, the second adhesive
portion 118A is displaced in a direction in which the second
adhesive portion 118A becomes distant from the second base
plate-fixing portion 114D. This direction is a direction opposite
to a direction in which the second adhesive portion 118A is
displaced due to the expansion of the base 114, and is a direction
approaching the first adhesive portion 116A. That is, since the
second base plate 118 is displaced so as to offset the displacement
of the base 114 when temperature is changed, an interval between
the first and second adhesive portions 116A and 118A can be always
maintained constant. Accordingly, since a force acting between the
first and second prism blocks 120 and 122 of the total reflection
prism 112 can be offset, the peeling of the bonding portion from
the first and second prism blocks 120 and 122 can be prevented.
Further, since both the first and second prism blocks 120 and 122
are supported in the prism unit 110 of this embodiment, the total
reflection prism 112 can be supported in a stable state.
Furthermore, since the first and second adhesive portions 116A and
118A are disposed close to each other in the prism unit 110 of this
embodiment, an influence of thermal expansion can be minimized.
Even in the prism unit 110 of this embodiment, the second base
plate 118 can include a first component and a second component as
described in the second embodiment. Accordingly, the prism unit can
be made to have a structure that is stronger against a change in
temperature.
Other Embodiments
A case in which the prism unit according to the invention is built
in a 3-plate type camera and a case in which the prism unit
according to the invention is built in a projection display device
have been described in the above-mentioned embodiments by way of
example, but the application of the invention is not limited
thereto. Further, the prism to which the invention is applied is
also not limited to the color separation prism and the total
reflection prism. A composite prism, which includes a plurality of
prisms bonded to each other, can be applied likewise. For example,
the invention can also be applied to a color synthesis prism having
the same structure as the color separation prism. Particularly, the
invention effectively acts on a composite prism in which prisms are
bonded to each other with an air layer interposed therebetween.
In the above-mentioned embodiments, the frame-shaped spacer has
been used when the prisms are bonded to each other with an air
layer interposed therebetween. However, the shape of the spacer is
not limited thereto.
FIGS. 11A and 11B are views showing other embodiments of the
spacer, respectively (corresponding to a cross-sectional view of
the bonding portion between the first and second prism blocks).
A form shown in FIG. 11A is a form in which the spacer 26 includes
four rectangular plate pieces 26A and the respective plate pieces
26A are disposed at four corners of the bonding surface.
A form shown in FIG. 11B is a form in which the spacer 26 includes
four long plate pieces 26B and each of the plate pieces 26B is
disposed in the middle of each of four sides of the bonding
surface.
In all of the forms, the spacer 26 is disposed in a region other
than a region including the optical axis OP. Accordingly, the first
and second prism blocks are bonded to each other so that an air
layer is formed in the region including the optical axis OP.
Further, a composite prism in which the first and second prism
blocks are bonded to each other with the air layer interposed
therebetween has been described in the above-mentioned embodiments
by way of example, but the invention can also be applied to a
composite prism in which first and second prism blocks are
gaplessly bonded to each other.
Example
Verification of Effect of the Invention
The following verification experiments have been performed to
verify the effects of the invention.
In the prism unit having the structure shown in FIG. 1, the
condition of
".alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T" was changed
by the change of the distance L between the first base plate-fixing
portion 14C and the second base plate-fixing portion 14D and the
distance M between the second base-fixing portion 18B and the
second adhesive portion 18A, and a predetermined environmental test
was performed for each condition.
In the environmental test, an operation for heating a prism unit up
to 70.degree. C. from the room temperature (25.degree. C.) for 30
minutes and cooling the prism unit to the room temperature
(25.degree. C.) for 30 minutes after leaving the prism unit under
the condition of 70.degree. C. for 2 hours was performed in a
constant-temperature tank as one cycle.
The material of the base 14 of the prism unit was set to stainless
steel, the material of the second base plate 18 was set to an
aluminum alloy, and the material of the prism of the color
separation prism 12 was set to BK7 as optical glass.
The linear expansion coefficient .alpha. of the base 14 made of
stainless steel was 1.7.times.10.sup.-5 (exponent notation:
1.7E-5), the linear expansion coefficient (equivalent linear
expansion coefficient) .beta. of the second base plate 18 made of
an aluminum alloy was 2.4.times.10.sup.-5 (exponent notation:
2.4E-5), and the linear expansion coefficient (equivalent linear
expansion coefficient) .gamma. of the color separation prism 12
made of optical glass (BK7) was 7.1.times.10.sup.-6 (exponent
notation: 7.1E-6). Accordingly, the condition of
".alpha.<.beta." was satisfied.
Further, an epoxy resin adhesive was used as the adhesive.
The following conditions A to K were set in regard to the condition
of ".alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T".
Condition A: L=10.8 mm, M=7.0 mm, (L-M)=3.8 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-5.2.times.10.sup.--
4
Condition B: L=11.0 mm, M=7.0 mm, (L-M)=4.0 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-4.5.times.10.sup.--
4
Condition C: L=11.1 mm, M=7.0 mm, (L-M)=4.1 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-4.0.times.10.sup.--
4
Condition D: L=11.7 mm, M=7.0 mm, (L-M)=4.7 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-9.3.times.10.sup.--
5
Condition E: L=11.9 mm, M=7.0 mm, (L-M)=4.9 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-4.5.times.10.sup.--
5
Condition F: L=12.0 mm, M=7.0 mm, (L-M)=5.0 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-2.2.times.10.sup.--
5
Condition G: L=12.1 mm, M=7.0 mm, (L-M)=5.1 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-4.4.times.10.sup.--
5
Condition H: L=12.2 mm, M=7.0 mm, (L-M)=5.2 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-9.6.times.10.sup.--
5
Condition I: L=12.9 mm, M=7.0 mm, (L-M)=5.9 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-4.0.times.10.sup.--
4
Condition J: L=13.0 mm, M=7.0 mm, (L-M)=6.0 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-4.6.times.10.sup.--
4
Condition K: L=13.2 mm, M=7.0 mm, (L-M)=6.2 mm
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T=-5.4.times.10.sup.--
4
FIG. 12 is a table showing results of verification experiments
about effects.
As shown in FIG. 12, it is possible to confirm that the prism unit
can be made to have a structure stronger against a change in
temperature when the prism unit is set so that the value of
".alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T" as a change
in interval is within the range of .+-.4.times.10.sup.-4.
EXAMPLES
Example 1
In a case in which the material of the base 14 is set to stainless
steel, the material of the second base plate 18 is set to an
aluminum alloy, and the material of the prism of the color
separation prism 12 is set to BK7 as optical glass in the prism
unit having the structure shown in FIG. 1, it is possible to
prevent the peeling of the bonding portion between the first and
second prism blocks 20 and 22 by setting the first base
plate-fixing portion 14C, the second base plate-fixing portion 14D,
the second base-fixing portion 18B, and the second adhesive portion
18A so that the following conditions are satisfied. That is, in a
case in which a distance between the first and second base
plate-fixing portions 14C and 14D is denoted by L and a distance
between the second base-fixing portion 18B and the second adhesive
portion 18A is denoted by M, the first base plate-fixing portion
14C, the second base plate-fixing portion 14D, the second
base-fixing portion 18B, and the second adhesive portion 18A are
set so that L is 12 mm and M is 7.03 mm.
Accordingly, since the conditions of ".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4" can be satisfied, the peeling of
the bonding portion between the first and second prism blocks 20
and 22, which is caused by a change in temperature, can be
prevented.
That is, in a case in which the material of the base 14 is set to
stainless steel, the material of the second base plate 18 is set to
an aluminum alloy, and the material of the prism of the color
separation prism 12 is set to BK7 as optical glass, the linear
expansion coefficient .alpha. of the base 14 (stainless steel) is
1.7.times.10.sup.-5, the linear expansion coefficient (equivalent
linear expansion coefficient) .beta. of the second base plate 18
(aluminum alloy) is 2.4.times.10.sup.-5, and the linear expansion
coefficient (equivalent linear expansion coefficient) .gamma. of
the color separation prism 12 (optical glass (BK7)) is
7.1.times.10.sup.-6. Accordingly, the condition of
".alpha.<.beta." is satisfied.
When the distance L between the first and second base plate-fixing
portions 14C and 14D is set to 12 mm, the distance M between the
second base-fixing portion 18B and the second adhesive portion 18A
is set to 7.03 mm, and a change .DELTA.T in temperature is set to
45.degree. C. (70.degree. C. from 25.degree. C.),
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T is
-3.1.times.10.sup.-7 and the condition of
"-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).-
DELTA.T.ltoreq.4.times.10.sup.-4" is also satisfied (more
preferable condition (.+-.5.times.10.sup.-5) is also
satisfied).
Accordingly, in a case in which the material of the base 14 is set
to stainless steel, the material of the second base plate 18 is set
to an aluminum alloy, and the material of the prism of the color
separation prism 12 is set to BK7 as optical glass in the prism
unit having the structure shown in FIG. 1, it is possible to
prevent the peeling of the bonding portion between the first and
second prism blocks 20 and 22, which is caused by a change in
temperature, by setting the first base plate-fixing portion 14C,
the second base plate-fixing portion 14D, the second base-fixing
portion 18B, and the second adhesive portion 18A so that L is 12 mm
and M is 7.03 mm.
Example 1 corresponds to Condition F of the verification
experiments. It is possible to confirm that the prism unit of
Example 1 has a structure strong against a change in temperature
from the results of the verification experiments.
Example 2
In a case in which the material of the base 14 is set to titanium,
the material of the second base plate 18 is set to stainless steel,
and the material of the prism of the color separation prism 12 is
set to BK7 as optical glass in the prism unit having the structure
shown in FIG. 1, it is possible to prevent the peeling of the
bonding portion between the first and second prism blocks 20 and 22
by setting the first base plate-fixing portion 14C, the second base
plate-fixing portion 14D, the second base-fixing portion 18B, and
the second adhesive portion 18A so that the following conditions
are satisfied. That is, in a case in which a distance between the
first and second base plate-fixing portions 14C and 14D is denoted
by L and a distance between the second base-fixing portion 18B and
the second adhesive portion 18A is denoted by M, the first base
plate-fixing portion 14C, the second base plate-fixing portion 14D,
the second base-fixing portion 18B, and the second adhesive portion
18A are set so that L is 12 mm and M is 1.58 mm.
Accordingly, since the conditions of ".alpha.<.beta. and
-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).D-
ELTA.T.ltoreq.4.times.10.sup.-4" can be satisfied, the peeling of
the bonding portion between the first and second prism blocks 20
and 22, which is caused by a change in temperature, can be
prevented.
That is, in a case in which the material of the base 14 is set to
titanium, the material of the second base plate 18 is set to
stainless steel, and the material of the prism of the color
separation prism 12 is set to BK7 as optical glass, the linear
expansion coefficient .alpha. of the base 14 (titanium) is
8.4.times.10.sup.-6, the linear expansion coefficient (equivalent
linear expansion coefficient) of the second base plate 18
(stainless steel) is 1.7.times.10.sup.-5, and the linear expansion
coefficient (equivalent linear expansion coefficient) .gamma. of
the color separation prism 12 (optical glass (BK7)) is
7.1.times.10.sup.-6. Accordingly, the condition of
".alpha.<.beta." is satisfied.
When the distance L between the first and second base plate-fixing
portions 14C and 14D is set to 12 mm, the distance M between the
second base-fixing portion 18B and the second adhesive portion 18A
is set to 1.58 mm, and a change .DELTA.T in temperature is set to
45.degree. C. (70.degree. C. from 25.degree. C.),
.alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).DELTA.T is
-1.9.times.10.sup.-6 and the condition of
"-4.times.10.sup.-4.ltoreq..alpha.L.DELTA.T-.beta.M.DELTA.T-.gamma.(L-M).-
DELTA.T.ltoreq.4.times.10.sup.-4" is also satisfied (more
preferable condition (.+-.5.times.10.sup.-5) is also
satisfied).
Accordingly, in a case in which the material of the base 14 is set
to titanium, the material of the second base plate 18 is set to
stainless steel, and the material of the prism of the color
separation prism 12 is set to BK7 as optical glass in the prism
unit having the structure shown in FIG. 1, it is possible to
prevent the peeling of the bonding portion between the first and
second prism blocks 20 and 22, which is caused by a change in
temperature, by setting the first base plate-fixing portion 14C,
the second base plate-fixing portion 14D, the second base-fixing
portion 18B, and the second adhesive portion 18A so that L is 12 mm
and M is 1.58 mm.
COMPARATIVE EXAMPLES
Comparative Example 1
A change in the interval of the bonding portion between the first
and second prism blocks 20 and 22, which is obtained in a case in
which the color separation prism 12 (composite prism) having the
structure shown in FIG. 1 is bonded to a base plate made of
stainless steel at two positions, is as follows.
(E-.gamma.)D.DELTA.T=0.005346
Here, E denotes the linear expansion coefficient of the base plate
made of stainless steel, and E is 1.7.times.10.sup.-5. Further, y
denotes the linear expansion coefficient of the color separation
prism 12, and .gamma. is 7.1.times.10.sup.-6. Furthermore, D
denotes a distance between the adhesive portions, and D is 12 mm.
Moreover, .DELTA.T denotes a change in temperature up to 70.degree.
C. from 25.degree. C., and .DELTA.T is 45.degree. C.
In this case, a change in the interval of the bonding portion
between the first and second prism blocks 20 and 22 may exceed
.+-.4.times.10.sup.-4, which is the allowable range thereof, and
the bonding portion may be peeled.
Comparative Example 2
A change in the interval of the bonding portion between the first
and second prism blocks 20 and 22, which is obtained in a case in
which the color separation prism 12 (composite prism) having the
structure shown in FIG. 1 is bonded to a base plate made of an
aluminum alloy at two positions, is as follows.
(Z-.gamma.)D.DELTA.T=0.009126
Here, Z denotes the linear expansion coefficient of the base plate
made of an aluminum alloy, and Z is 2.4.times.10.sup.-5. Further,
.gamma. denotes the linear expansion coefficient of the color
separation prism 12, and .gamma. is 7.1.times.10.sup.-6.
Furthermore, D denotes a distance between the adhesive portions,
and D is 12 mm. Moreover, .DELTA.T denotes a change in temperature
up to 70.degree. C. from 25.degree. C., and .DELTA.T is 45.degree.
C.
Even in this case, a change in the interval of the bonding portion
between the first and second prism blocks 20 and 22 may exceed
.+-.4.times.10.sup.-4, which is the allowable range thereof, and
the bonding portion may be peeled.
Comparative Example 3
A change in the interval of the bonding portion between the first
and second prism blocks 20 and 22, which is obtained in a case in
which the color separation prism 12 (composite prism) having the
structure shown in FIG. 1 is bonded to a base plate made of
titanium at two positions, is as follows.
(H-.gamma.)D.DELTA.T=0.000702
Here, H denotes the linear expansion coefficient of the base plate
made of titanium, and H is 8.4.times.10.sup.-6. Further, .gamma.
denotes the linear expansion coefficient of the color separation
prism 12, and .gamma. is 7.1.times.10.sup.-6. Furthermore, D
denotes a distance between the adhesive portions, and D is 12 mm.
Moreover, .DELTA.T denotes a change in temperature up to 70.degree.
C. from 25.degree. C., and .DELTA.T is 45.degree. C.
Even in this case, a change in the interval of the bonding portion
between the first and second prism blocks 20 and 22 may exceed
.+-.4.times.10.sup.-4, which is the allowable range thereof, and
the bonding portion may be peeled.
When a composite prism is bonded to one base plate as described
above, the bonding portion of the prism may be peeled due to a
change in temperature. However, it is possible to effectively
prevent the peeling of the bonding portion of the prism by
employing the invention.
EXPLANATION OF REFERENCES
1: 3-plate type camera 2: camera body 2A: bolt hole 3R, 3G, 3B:
imaging element 3r, 3g, 3b: light-receiving surface 4: lens mount
10: prism unit 10A: prism unit 12: color separation prism 14: base
14A: leg portion 14a: bolt insertion hole 14B: prism support
portion 14C: first base plate-fixing portion 14D: second base
plate-fixing portion 16: first base plate 16A: first adhesive
portion 16B: first base-fixing portion 16a: first prism-adhesive
surface 16b: first base-fixing surface 18: second base plate 18A:
second adhesive portion 18B: second base-fixing portion 18C: first
component 18D: second component 18a: second prism-adhesive surface
18b: second base-fixing surface 20: first prism block 20S: base
plate-installation surface 20a: imaging light-incident surface 20b:
blue light-reflecting surface 20c: blue light-emitting surface 22:
second prism block 22A: prism 22B: prism 22S: base
plate-installation surface 22a: incident surface 22b: red
light-reflecting surface 22c: red light-emitting surface 22d: green
light-emitting surface 24: air layer 26: spacer 26A: plate piece
26B: plate piece 28: base fixing bolt 30: first bolt 32: second
bolt 100: projection display device 101: light source 102: relay
lens 103: total reflection mirror 104: field lens 105: reflective
light valve 106: projection lens 107: device body 107A: bolt hole
110: prism unit 112: total reflection prism 114: base 114A: leg
portion 114B: prism support portion 114C: first base plate-fixing
portion 114D: second base plate-fixing portion 114a: bolt insertion
hole 116: first base plate 116A: first adhesive portion 116B: first
base-fixing portion 116a: first prism-adhesive surface 116b: first
base-fixing surface 118: second base plate 118A: second adhesive
portion 118B: second base-fixing portion 118a: second
prism-adhesive surface 118b: second base-fixing surface 120: first
prism block 120S: base plate-installation surface 122: second prism
block 1225: base plate-installation surface 124: air layer 126:
spacer 128: base fixing bolt 130: first bolt 132: second bolt OL:
optical axis of imaging lens OP: optical axis
* * * * *